For example, in a turbo refrigerator which is provided with a turbo compressor having a motor and an impeller, a refrigerant is compressed by the impeller, and therefore, the impeller side has a high pressure and the motor side relatively has a low pressure. If such a pressure difference is generated, gas leaks out from the high pressure side to the low pressure side, and therefore, it is necessary to perform sealing by a sealing mechanism. However, the impeller and the motor are connected by a rotating shaft for transmitting power, and therefore, it is difficult to completely isolate the high pressure side and the low pressure side from each other.
Therefore, as shown in, for example, Patent Document 1, in general, the leakage of gas along a rotating shaft is prevented by using a non-contact type labyrinth sealing mechanism which is fixed to a housing and disposed on the circumferential surface of the rotating shaft with a slight gap therebetween.
Further, Patent Document 2 discloses a mechanism for preventing the contact between a rotating shaft and a labyrinth seal by moving the labyrinth seal with respect to the rotating shaft in a radial direction of the rotating shaft, thereby narrowing the gap between the rotating shaft and the labyrinth seal at the time of a steady operation of the rotating shaft and widening the gap at the time of the starting and stopping of the rotating shaft.
Further, Patent Document 3 discloses a mechanism for preventing the contact between a rotating shaft and a labyrinth seal by moving the labyrinth seal with respect to the rotating shaft in an axial direction of the rotating shaft, thereby narrowing the gap between the rotating shaft and the labyrinth seal at the time of a steady operation of the rotating shaft and widening the gap at the time of the starting of the rotating shaft.